US3701659A - Photolithographic masks of semiconductor material - Google Patents

Photolithographic masks of semiconductor material Download PDF

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Publication number
US3701659A
US3701659A US42344A US3701659DA US3701659A US 3701659 A US3701659 A US 3701659A US 42344 A US42344 A US 42344A US 3701659D A US3701659D A US 3701659DA US 3701659 A US3701659 A US 3701659A
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Prior art keywords
mask
silicon
layer
semiconductor material
semiconductor
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Expired - Lifetime
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US42344A
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English (en)
Inventor
Ven Y Doo
Joseph Regh
David K Seto
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International Business Machines Corp
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International Business Machines Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/54—Absorbers, e.g. of opaque materials

Definitions

  • FIG. 2A SILICON
  • I 32 38 QUARTZ
  • g 36 4;? 4 PHOTO FIG. 2B RESIST
  • a photolithographic mask comprising a substrate of quartz or glass and a pattern-defining layer of a semiconductor material such as silicon.
  • the pattern is defined in the semiconductor material by etching of the semiconductor, involving displacement of the semicon ductor in selected areas with a metal such as copper. In this way, a high resolution mask is obtainable having the added feature of being partially transparent.
  • This invention relates to photolithographic techniques as these are employed in the manufacture of semiconductor integrated circuits and more particularly, to an improvement which yields a superior photographic or photolithographic mask.
  • integrated circuits encompasses a wide variety of techniques and forms which have been developed in the field of microcircuitry over the past decade.
  • the planar microcircuit technology is practiced.
  • the devices forming a complex circuit are embedded within the wafer by means of diffusion from the upper surface of the semiconductor wafer and interconnections between devices are made by metalization of the upper surface.
  • photolithographic techniques are utilized which involve as many as seven masks in performing the sequence of steps necessary to embed the devices within the monolith and to interconnect the devices by metalization.
  • the aforesaid photolithographic techniques enable the ready accomplishing of preferential oxide etching which is essential in producing the sequence of diffusion operations.
  • the wafer is coated with a photoresist in which a desired circuit pattern is developed by exposing selected areas of the photoresist whereby the oxide layer underlying the photoresist can be selectively attacked.
  • a photographic or photolithographic mask is either a positive or negative image of a circuit pattern formed on a photosensitized glass plate.
  • a photolithographic mask usually comprises a matrix or substrate of glass or similar material and a layer of photo emulsion, or in some cases a layer of chromium or the like, in which the circuit pattern is defined.
  • the purpose of a photolithographic mask is the formation of a resist mask, the purpose of the latter being to selectively etch the oxide or metal that it covers.
  • the so-called oxide mask is defined by a selectively etched pattern of openings in the oxide which permits the selective diffusion of impurities into the wafer.
  • the present invention resides in an improvement in the photolithographic mask used to create the desired pattern in the resist mask.
  • the improved photolithographic mask comprises a substrate of quartz or glass and a deposited layer thereon of finegrained amorphous silicon or silicon-germanium alloy, the semiconductor layer having etched out portions which have been replaced with a metal such as copper, thereby to produce the desired masking pattern.
  • the selection of a silicon-germanium alloy takes advantage of the Wide range of the wavelengths, which provides a high absorption coefl icient.
  • the present invention embraces the technique for producing the aforesaid photolithographic mask comprising the essential steps of depositing a layer of semiconductor material on a quartz or glass substrate and photolithographically etching the semiconductor material by means of a copper displacement chemical reaction to produce the requisite mask-defining openings in the semiconductor material.
  • the improved mask will be able to Withstand usage involving contact with an uneven silicon wafer. This is in contrast to the photo emulsion type of mask which is not able to take such contact due to the softness of the emulsion.
  • the metal displacement etching technique which is advantageously utilized in conjunction with the semiconductor pattern-defining layer, permits the creation of openings in the silicon, or similar semiconductor layer having extremely sharp edges, this being in contrast with the openings obtained in photo emulsion layers.
  • FIG. 1 is a sectional view illustrating the general photolithographic technique known in the prior art.
  • FIGS. 2A, 2B, 2C and 2D are perspective views illustrating the several steps in accordance with the technique of the present invention for producing a photolitho graphic mask.
  • FIG. 1 there is illustrated the general photolithographic technique known in the art.
  • a photolithographic mask 10 comprising a substrate 12 of glass or the like, and a pattern-defining layer 14 consisting of a photo emulsion material or chromium, is disposed in spatial relationship to a semiconductor structure 16.
  • the structure 16 comprises a semiconductor wafer 18, the upper surface of which is coated with an oxide layer 20, for the purposes of selective diffusion; and superposed on the oxide layer as a photoresist layer 22.
  • the photolithographic mask 30 comprises a substrate 32 of quartz or glass upon which there has been deposited a layer 34, which is either constituted of silicon or a silicon-germanium alloy.
  • the layer 34 can be achieved in a variety of ways such as by vapor growth onto the surface of the substrate 32.
  • the vapor growth technique is well-known in the art, and can be appreciated by reference to U.S. Pat. 2,993,- 762. Such a technique involves, for the preferred example, the pyrolysis of silane at a temperature of approximately 700 C. or below.
  • the silicon layer 34 should have a thickness of less than 2500 A.
  • the next step in the procedure for achieving the unique photolithographic mask is to coat the already deposited silicon layer 34 with a layer 36 of photoresist material such as KTFR (material sold by Eastman-Kodak)
  • KTFR material sold by Eastman-Kodak
  • the photoresist material is then exposed to the pattern which it is desired to create for the mask 30, and as is conventional following such exposure, the unalfected portions of the photoresist are washed away, with the result as depicted in FIG. 2B of a desired pattern of openings 38 in the photoresist.
  • aqueous displacement plating solutions contain a cupric cation and fluoride anion and have a pH of less than 7. It has been found that ultrasonic agitation during this etching step enhances the etching of the silicon.
  • the effect of the copper displacement of the silicon atoms can be seen in FIG. 20.
  • the copper is completely washed away by rinsing the wafer. However, if any residual copper remains it can be removed by a nitric acid solution. The nitric acid also acts to destroy or dissolve the remaining photoresists.
  • the resulting structure is as illustrated in FIG. 2D in which it will be seen that the pattern of openings 42 corresponds with the selective displacement of silicon by the copper at the areas 40 which, in turn, corresponds with the selected openings 38 in the photoresists, i.e. to those areas where the photoresist was removed, thereby allowing etching of the silicon.
  • a final stripping in acetone can be carried out so as to remove any residual photoresist. Subsequently, a rinse in alcohol and drying in a warm air stream can be carried out in the event the acetone is the solvent that has been used.
  • the fundamental advantage of the copper displacement etching step resides in the fact that it does not attack the photoresist layer 36.
  • a further I advantage is that below approximately 2000 A. of silicon thickness the copper layer formed during the displacement etch appears to suppress lateral etching (undercutting) and yields a preferential etch through the film thickness. This is especially true when ultrasonic agitation enhances the removal of copper as it displaces the silcon. However, in those cases where the silicon layers were of a thickness of approximately 4000 A., undercutting was observed.
  • a spectrograph analysis reveals an absorption edge of 4200-5800 A. This absorption renders transmitted white light as reddish tinged. Therefore, yellow or green and longer wavelength filtered light can be utilized during superposed alignment. The adsorption edge is also convenient since most photoresists are sensitive. to light of wavelength shorter than 4800 A.
  • the substrate was indicated to be constituted of quartz, and thesemiconductor material utilized therewith was silicon, and numerous experiments have been conducted utilizing these materials.
  • other semiconductor materials can serve equally as well.
  • a silicon-germanium alloy can be employed, and, in particular, can be deposited onto glass in order to provide a suitable photolithographic mask by a reaction such as simple pyrolysis or by other low temperature vapor growth reactions.
  • silicon be deposited by radio-frequency sputtering.
  • silicon was sputtered onto 2 /2" x 2 /2" glass plates to a thickness of approximately 1200 A., where the substrate was heated to 300 C. for adhesion enhancement.
  • a photolithographic mask comprising a substrate of quartz of glass and a thin, pattern-defining layer of semiconductor material formed on the substrate, the pattern being defined in the semiconductor material by displacement etching of the semiconductor layer.
  • a process of fabricating a photolithographic mask comprising:
  • a patterned resist mask on the surface of said thin layer by coating said thin layer with a layer of photoresist, and then exposing and developing the photoresist layer,

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Preparing Plates And Mask In Photomechanical Process (AREA)
US42344A 1970-06-01 1970-06-01 Photolithographic masks of semiconductor material Expired - Lifetime US3701659A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4264551A (en) * 1978-08-25 1981-04-28 Matsushita Electrical Industrial Co., Ltd. Recorded disk reproducing system
US4567576A (en) * 1981-10-02 1986-01-28 Shin-Etsu Chemical Co., Ltd. Method for producing a magnetic bias field
US6039168A (en) 1971-04-16 2000-03-21 Texas Instruments Incorporated Method of manufacturing a product from a workpiece

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1031978A (en) * 1964-11-06 1966-06-02 Standard Telephones Cables Ltd Improvements in or relating to photolithographic masks

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6039168A (en) 1971-04-16 2000-03-21 Texas Instruments Incorporated Method of manufacturing a product from a workpiece
US6076652A (en) 1971-04-16 2000-06-20 Texas Instruments Incorporated Assembly line system and apparatus controlling transfer of a workpiece
US6467605B1 (en) 1971-04-16 2002-10-22 Texas Instruments Incorporated Process of manufacturing
US4264551A (en) * 1978-08-25 1981-04-28 Matsushita Electrical Industrial Co., Ltd. Recorded disk reproducing system
US4567576A (en) * 1981-10-02 1986-01-28 Shin-Etsu Chemical Co., Ltd. Method for producing a magnetic bias field

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FR2093930A1 (enExample) 1972-02-04
FR2093930B1 (enExample) 1974-06-21

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